Functioning kidneys of the mammals remove excess fluids, electrolytes, and other molecules. In patients with Chronic Kidney Disease (CKD), kidney function is severely compromised. Chronic kidney disease (CKD), also known as chronic renal disease, is a progressive loss in renal function over a period of months or years. The co-morbidities of CKD are diabetes and high blood pressure, which are indicated to be responsible for up to two-thirds of the cases. Heart disease and the associated cardiac arrhythmias are the leading cause of death for many people suffering from CKD. Excessive fluid, ions and other toxins accumulate in patients with CKD. Although these patients are usually treated by hemodialysis therapy, the treatment is not continuous, but periodic, causing the build-up of excessive amount of fluids in the body between hemodialysis sessions.
Fluid buildup in the body is also a concern for patients with heart failure, a debilitating medical condition in which the ability of the heart muscle to pump the blood is reduced. As the contractions of the heart become weaker and the ability of the heart to push the blood into the arteries is reduced, both the stroke volume and the cardiac output decrease. The volume of blood remaining in the veins increase, causing the fluid to build in the tissues of the subject. The ability of the kidney to excrete excess salts and water is also reduced during the heart failure, further increasing the overall fluid accumulation. Excess fluid can build up in various locations in the body, leading to a general condition known as edema. Edema may cause the swelling that occurs in the feet, ankles and the legs, in which case it is called the peripheral edema. It may also occur in the lungs as with pulmonary edema or in the abdomen as in ascites.
Fluid accumulation in the body causes multiple problems for the patient and the health care system. Peripheral edema causes local pain and discomfort. Pulmonary edema creates breathing difficulties and makes it difficult for the patients to sleep. Ascites increases the external pressure on the vena cava, resulting in the reduced blood return to the heart from the systemic circulation. The increased blood volume elevates the load on the already weakened cardiac muscle, making the heart failure even worse. The increased blood volume also increases the systolic blood pressure which worsens the kidney failure. The stretching of the thin walls of the atria due to the excess blood volume increases the incidence of atrial fibrillation. Given all the negative effects of the volume overload, fluid overload in the patients, especially for ones with kidney or heart disease, must be managed carefully. Otherwise, patients require frequent hospitalizations, which is inconvenient and costly to medical system.
Over the years, many methods have been developed to treat the fluid overload in patients suffering from cardiac and kidney failure. The methods range from pharmaceutical therapies such as the administration of diuretics to increase urine production by the kidneys to the physical methods to directly remove fluids such as ultrafiltration, hemodialysis and peritoneal dialysis. Diuretics increase the urine production by the kidneys to enhance the removal of the fluids using the residual function of the renal system. Although using diuretics reduces the fluid volumes, some patients do not respond to this therapy, either due to the resistance of their body to the drug, or due to the complete failure of their kidneys. Diuretics also contribute to a phenomenon known as the downward spiral in patients with heart failure as illustrated in FIG. 1. Briefly, the administration of diuretics 101 initially leads to the reductions in the fluid volume 102. As the fluid volume is decreased, the venous pooling of the blood is also reduced, providing some relief to the heart 103. The filling of the heart is also reduced 104 due to the lower pressure of blood in the venous system. Since the heart is not filled completely, cardiac muscle is not fully stretched; hence it does not contract vigorously, but instead produces a weak ejection 105 and 106. This once again causes increased fluid accumulation 107 in the lungs and in the other tissues, leading to the worsening of the forward heart failure 108, which is the inability of the heart to deliver adequate amounts of blood into the arteries. After repeating the cycle in FIG. 1 many times, diuretics eventually become ineffective and the symptoms of the patient can no longer be treated with the administration of additional diuretics. The situation is further illustrated in FIG. 2 where the venous return 201 and cardiac output 202 are shown as a function of the right atrial pressure 203. In that diagram, the normal venous return 204 and cardiac output 205 are shown at point 206. Fluid overload elevates the right atrial pressure, resulting in the reduction of both the venous return and the cardiac output of the patient to the point at 207. Chronic stretching of the atrial wall due to the excess fluid volumes and the increased atrial pressures lead to the onset of cardiac arrhythmias, usually in the form of atrial fibrillation.
Hence, there is a need for methods and systems that overcome the limitations of diuretics. There is also a need for methods and systems to treat the fluid overload in patients suffering from cardiac and kidney failure that overcome limitations associated with pharmaceutical therapies and physical methods to directly remove fluids such as ultrafiltration, hemodialysis and peritoneal dialysis.